A general receiver adopting a super-heterodyne method converts a frequency by using a frequency mixing circuit after amplifying a modulated wave signal received via an antenna at a high frequency, and demodulates it after converting it into an intermediate-frequency signal having a predetermined frequency.
Furthermore, progress has recently been made on the research of techniques of integrally forming the constituent components of a receiver on a semiconductor using a CMOS process or a MOS process. By thus molding various circuits on one chip using the CMOS process or MOS process, it is possible to reduce the size and cost of the whole device. Accordingly, the range of circuits molded on one chip is expected to be increased in the future.
With respect to an output from an oscillator, focus will be on its frequency components. As shown in FIG. 10, noise side bands appear at the opposite sides of an ideal output spectrum with a frequency f0. The noise side bands are composed of ideal oscillator spectrum components on which 1/f noises that are low frequency noises are superimposed and consist mainly of phase noises and frequency noises. In particular, a MOS type FET has more 1/f noises than a bipolar transistor and thus has more noise side bands appearing in the output of the oscillator. Consequently, when such an oscillator is used as a local oscillator, many noise components are superimposed on an intermediate frequency signal obtained by a frequency conversion. This reduces an SN ratio to degrade the quality of reception.